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(Holt and Tattersall, 1905)

Description
— Generic features. Carpo-propodus divided into a variable number of subsegments. Eyes large and globular with short broad eyestalks.
Pleopods in both sexes reduced to simple unsegmented plates which become progressively longer ont eh posterior abdominal somites. Inner margin of endopod of uropod with a close row of spines from statocyst to distal end.
Telson not armed with spines along the entire margin and with apical cleft and 3-6 long apical spines; margins concave.
—Species. Carapace short, not much more than half as long as the abdomen; anterior margin produced forward inbo an obtusely rounded rostrum; antero-lateral angles rounded, posterior border emarginate, leaving the whole of the last, and most of the seventh, thoracic somites exposed in dorsal view.
Antennular peduncle robust; first and third segments subequal; middle segment very short.
Antennal scale long and narrow with the inner margin convex and the outer straight or slightly concave, setose all round; small distal suture present; spine on outer distal corner of sympod reduced or absent. The proportions of the length to the breadth vary with the size of the animals.
Eyes large globular, extending beyond the second segment of the antennular peduncle; pigment red.
Second thoracic limb with a definite expansion on the inner side of the second segment such as is found in many species of Mysidopsis. Third thoracic limb with endopod long and slender, carpopropodus three-segmented, the second and third subequal, dactylus very small; nail in larger specimens nearly equal in length to the sum of the two distal subsegments of the carpopropodus. In the larger specimens from northern waters the ischium, merus and carpopropodus are very profusely furnished with long plumose setae. Remaining thoracic limbs very long and slender, becoming progressively longer on the posterior somites in particular the first segment of the carpopropodus in the posterior limbs lengthens and may be as much as three times the combined length of the other two. Genital appendage of the eighth thoracic limb tubular, very long; extending forward along the ventral surface of the body as far as the mouthparts (so that the aperture at the distal end points downward). Pleopods as described for the genus.
Telson equal in length to the last abdominal somite, narrowing towards the apex where it is rather less than half its basal width; apex cleft to a depth varying from one-fifth to one-tenth of the total length of the telson; cleft rounded at its anterior end, widening somewhat posteriorly, armed with from three to six small teeth on each side, but without plumose setae, apical lobes armed with two spines, the inner of which is much less than half the length of the outer, lateral margins armed along the distal three-fifths of their length with from 10 - 26 spines according to the size of the specimen.
Uropods with exopod twice as long as, endopod about one and a half times as long as the telson, armed along the inner margin with from 25 - 28 spines which extend from the region of the statocyst to within a short distance of the apex, increasing slightly in length distally in the smaller race.

Size
Adults from southern waters, 10 mm; from British waters, 33 mm.

Depth range
Hyperbenthic. The species is a bottom-living form and is not uncommon at suitable. It is most abundant between 850-1050 m.

Remarks
This species may be distinguished from the others of the genus by the very short, triangular, obtusely rounded rostrum; the antennal scale which extends beyond the antennular peduncle, the reduction of the spines at the base of the antennal scale; the four-segmented tarsus of the endopods of the third to the eighth thoracic limbs; the length and armature of the endopods of the uropods and the shape and armature of the telson.

Distribution in the North Sea
Off Norway, Skagerrak, deep water.

World distribution
E North Atlantic 30-63°N, Mediterranean; slope.

[After Tattersall and Tattersall, 1951]

Mysidetes farrani